Photoresponsive delivery systems that are activated by high energy photo-triggers have been accorded much attention because of the capability to achieve reliable photoreactions at short irradiation times. However, the application of a high energy photo-trigger (UV light) is not clinically
viable. Meanwhile, the process of photon-upconversion is an effective strategy to generate a high energy photo-trigger (in-situ) through exposure to clinically relevant near-infrared (NIR) light. In this regard, we synthesized photon upconverting nanocrystals (UCNCs) that were subsequently
loaded into photoresponsive nanoparticles (NPs) that were prepared using alkoxyphenacyl-based polycarbonate homopolymer (UCNC-APP-NPs). UCNC loading affected resultant NP size, size distribution, colloidal stability but not the zeta potential. The efficiency of NIR-modulated drug delivery
was impacted by the heterogenetic nature of the resultant UCNC-APP-NPs which was plausibly formed through a combination of UCNC entrapment within the polymeric NP matrix and nucleation of polymer coating on the surface of the UCNCs. The biocompatibility of UCNC-APP-NPs was demonstrated through
cytotoxicity, macrophage activation, and red blood cell lysis assays. Studies in tumor-bearing (nu/nu) athymic mice showed a negligible distribution of UCNC-APP-NPs to reticuloendothelial tissues. Further, distribution of UCNC-APP-NPs to various tissues was in the order (highest to lowest):
Lungs > Tumor > Kidneys > Liver > Spleen > Brain > Blood > Heart. In all, the work highlighted some important factors that may influence the effectiveness, reproducibility and biocompatibility of drug delivery systems that operate on the process of photon-upconversion.

Journal for Nanoscience and Nanotechnology (JNN) is an international and multidisciplinary peer-reviewed journal with a wide-ranging coverage, consolidating research activities in all areas of nanoscience and nanotechnology into a single and unique reference source. JNN is the first cross-disciplinary journal to publish original full research articles, rapid communications of important new scientific and technological findings, timely state-of-the-art reviews with author's photo and short biography, and current research news encompassing the fundamental and applied research in all disciplines of science, engineering and medicine.